Stemless metaphyseal humeral implant

ABSTRACT

A stemless prosthetic shoulder joint may include a prosthetic humeral head and a stemless base. The stemless base may include a collar and an anchor extending from the collar intended to anchor the base into the proximal humerus. The anchor may include various features to enhance the fixation of the base, including hooks, threads, and/or expandable members that may be transitioned from a contracted insertion condition to an expanded implanted condition once the base is positioned in the bone. The anchor and/or collar may also include additional features to enhance fixation, such as geometries and surface features to enhance fixation to bone. The anchor may include a plurality of chisel slots to facilitate removal of bone during a revision surgery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This present application is a continuation of U.S. patent applicationSer. No. 17/372,600, filed Jul. 12, 2021, which is a continuation ofU.S. Pat. No. 11,076,962, filed Mar. 20, 2018, which claims the benefitof the filing date of U.S. Provisional Patent Application No.62/474,800, filed Mar. 22, 2017, and U.S. Provisional Patent ApplicationNo. 62/542,396, filed Aug. 8, 2017, the disclosures of which are herebyincorporated herein by reference as if fully set forth herein.

FIELD OF THE DISCLOSURE

The present application relates to a shoulder prosthesis, and inparticular to a humerus implant.

BACKGROUND OF THE DISCLOSURE

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on bones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., arthritis) can cause cartilage in joint areas, for example, whichnormally provides a cushioning effect, to wear down. When the cartilagewears down, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility. The same can happen in cases wheretendons in a joint become lax or soft tissues in or adjacent the jointbecome damaged or worn.

Arthroplasty procedures can be used to repair such damaged joints.During a typical arthroplasty procedure, an arthritic or otherwisedysfunctional joint can be remodeled or realigned. A prosthesis orprostheses can be implanted to repair the damaged region(s).Arthroplasty procedures may take place in any of a number of differentregions of the body, such as the knees, hips, shoulders, or elbows, forexample. One type of arthroplasty procedure is a shoulder arthroplasty,in which a damaged shoulder joint may be replaced with prostheticimplants. The shoulder joint may have been damaged by, for example,arthritis (e.g., severe osteoarthritis or degenerative arthritis),trauma, or a rare destructive joint disease.

Prostheses that are implanted into a damaged region may provide supportand structure to the damaged region, and may help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of aprosthesis in a damaged region, the damaged region may be prepared toreceive the prosthesis. In the case of a shoulder arthroplastyprocedure, one or more of the bones in the shoulder area, such as thehumerus and/or glenoid, may be treated (e.g., cut, drilled, reamed,and/or resurfaced) to provide one or more surfaces that can align withthe implant and thereby accommodate the implant.

It is often preferable to maintain as much of a patient's natural bonestock as possible during such a procedure. Prostheses generally have acertain life expectancy and in certain cases need to be replaced at somepoint. If one or more prostheses need to be removed and/or replaced in arevision procedure, a large bone void could be left after their removal.In certain cases, this bone void is not ideal for receipt of revisioncomponents. Preserving natural bone stock may be desirable for theability to even perform a revision procedure.

In total or partial arthroplasty surgery, stemmed prostheses are oftenused which generally include a long stem that passes through a center ofa long bone, the stem helping to anchor the remaining components of theprosthesis. However, stemmed prostheses may result in a large amount ofhealthy bone being removed in order to accommodate the stem. In somecases, stemless prostheses may be used, which may result in less healthybone stock being removed. However, in some cases stemless prostheses maynot anchor the particular prosthesis as well as a stemmed prosthesiswould. In additional, some stemless shoulder prostheses may require theremoval of significant proximal humeral bone, which may compromise theproximal humerus bone and result in more challenging revision surgeries.

BRIEF SUMMARY OF THE DISCLOSURE

According to one aspect of the disclosure, a base member of a stemlessshoulder implant includes a proximal collar and an anchor. The anchorextends distally from the collar along a longitudinal axis, the anchorextending from a first end coupled to the collar to a tip at a secondend of the anchor and having an outer wall having a plurality of peaksand a plurality of troughs. Each trough is adjacent to at least onepeak, and each peak extends farther radially outward of the longitudinalaxis than an adjacent one of the troughs. Each peak is adapted to engagea bone. The outer wall includes a flexible portion and a static portion,the flexible portion having an expanded condition in which the flexibleportion extends radially outwardly of adjacent surfaces of the staticportion and a constrained condition in which the flexible portion issubstantially flush with the adjacent surfaces of the static portion.The anchor may be tapered along the longitudinal axis. A recess may beadapted to receive an insertion or extraction instrument, wherein uponinsertion of the instrument into the recess, the flexible portiontransitions from the expanded condition to the constrained condition.The flexible portion may be adapted to transition from the constrainedcondition into the expanded condition upon removal of the instrumentfrom the recess. Each peak may transition into a proximally adjacenttrough at a proximally-facing hook. The flexible portion may be at leastpartially defined by a slot extending through the outer wall and may beadapted to allow for expansion of the flexible portion. The base mayinclude four of the flexible portions and four corresponding slotspositioned at substantially equal intervals around a circumference ofthe outer wall of the anchor.

According to another aspect of the disclosure, a base member of astemless shoulder implant includes a proximal collar, a central anchor,and a plurality of peripheral anchors. The proximal collar has aproximal surface, a bone-engaging surface, and a plurality of holesextending from the proximal surface to the bone-engaging surface. Thecentral anchor extends distally along a longitudinal axis of the basemember from the bone-engaging surface of the collar a first distance toa central tip and having a plurality of flutes extending toward the tip.The plurality of peripheral anchors are each positioned radiallyoutwardly of the central anchor and extend distally from thebone-engaging surface of the collar a second distance to a peripheraltip, the first distance being greater than the second distance. Theproximal surface of the collar may include an opening adapted to matewith a prosthetic humeral head component. At least a portion of thecentral anchor may include a porous metal surface. The peripheralanchors may include flutes extending from the bone-engaging surface tothe peripheral tip. A recessed groove may extend circumferentiallyaround at least a portion of the central anchor at the connection of thebone-engaging surface and the central anchor. Each flute on the centralanchor may include two edges extending from the proximal collar to thecentral tip, each edge having an apex extending a greater radialdistance from the longitudinal axis than any other portion of the edge.Each flute on the central anchor may include an enhanced fixationsurface extending from the recessed groove to a point circumferentiallyaligned with the adjacent apices, the enhanced surface including aporous metal surface. At least one of the plurality of holes may bepositioned adjacent the enhanced fixation surface on one of the flutes.At least one of the plurality of holes may be oblong with a major axisextending radially outwardly from the longitudinal axis. The at leastone hole may be positioned adjacent one of the peripheral anchors. Theplurality of peripheral anchors may include four peripheral anchorspositioned at substantially equal circumferential intervals around thecollar.

According to still another aspect of the disclosure, a base member of astemless shoulder implant includes an annular proximal collar, athreaded anchor, and a socket. The collar has a proximal surface, abone-engaging surface, and defines an open interior space. The anchorextends distally from the bone-engaging surface of the collar. Thesocket is positioned within the open interior space of the collar anddefines an opening extending from the proximal surface of the collar toa distal end of the anchor.

According to yet another aspect of the disclosure, a base member of astemless shoulder implant includes a proximal collar, an anchor, and arotatable nut. The collar has a proximal surface, a bone-engagingsurface, and a central opening extending along a longitudinal axis ofthe base member from the proximal surface to the bone-engaging surface.The anchor extends distally from the bone-engaging surface of the collarto a free end, the anchor having a plurality of flanges extending fromthe bone-engaging surface to the free end. Each flange has an innersurface with first threads and a distal tapered portion. The nut has anouter diameter and second threads adapted to engage the first threads ofthe flanges. The base member has a constrained condition in which thenut is positioned proximal to the distal tapered portions of the flangesand the distal tapered portions of the flanges define an internaldiameter less than the outer diameter of the nut. The base member alsohas an expanded condition in which the nut is radially aligned with thedistal tapered portions of the flanges. The base member transitions fromthe constrained condition to the expanded condition upon rotation of thenut, and rotation of the nut causes the nut to translate distally withrespect to the inner surfaces of the flanges. A support member mayextend distally from the bone-engaging surface to a distal surface ofthe support. When the nut is in contact with the distal surface of thesupport, the base member is in the constrained condition. The supportmember may include a central opening contiguous with the central openingof the collar.

According to still another aspect of the invention, a base member systemof a stemless shoulder implant includes a proximal collar, a centralanchor, and a plurality of screws. The proximal collar has a proximalsurface, a bone-engaging surface, and a plurality of holes extendingfrom the proximal surface to the bone-engaging surface. The centralanchor extends distally along a longitudinal axis of the base memberfrom the bone-engaging surface of the collar a first distance to acentral tip. The plurality of screws are adapted to be received in theplurality of holes, at least one of the plurality of screws having adifferent length than another of the plurality of screws.

In yet another aspect of the present disclosure, a base member of astemless shoulder implant includes a proximal collar that has a proximalsurface and a bone-engaging surface opposite the proximal surface, acentral anchor that extends distally along a longitudinal axis of thebase member from the bone-engaging surface of the collar a firstdistance to a central tip. The central anchor has a plurality of ribsthat extend toward the central tip. The base member includes at leastone chisel slot extending from the bone-engaging surface to the proximalsurface adjacent a portion of the central anchor. The chisel slot isconfigured to receive a tool for removing bone.

In other embodiments, the collar of the base member may define a firsthole and a second hole, both holes extending from the proximal surfaceto the bone-engaging surface. The first hole may have a first diameterand the second hole may have a second diameter, the second diameterbeing greater than the first diameter. The first hole may be configuredto receive a variable angle screw, and the second hole may be configuredto receive a fixed angle screw. The first hole may be positionedsuperior to the second hole when implanted. The plurality of ribs mayinclude four ribs positioned in a substantially “X”-shapedconfiguration. A first rib may be positioned about 60 degrees from asecond rib and about 120 degrees from a third rib, the third rib may bepositioned about 60 degrees from a fourth rib, and the second rib may bepositioned about 120 degrees from the fourth rib. The chisel slot mayhave a substantially “M”-shaped configuration. The first hole may bepositioned between the first and second ribs and the second hole may bepositioned between the third and fourth holes. At least one peripheralanchor may be positioned radially outward of the chisel slot. In otherembodiments, the base member may form a system with a chisel tool. Thechisel tool may have a shaft extending along a longitudinal axis and acutting structure connected to a distal end of the shaft, the cuttingstructure may be sized and configured to fit within at least a portionof the chisel slot of the base. The cutting structure may have asubstantially “M”-shaped configuration. The cutting structure may have adistal surface having a plurality of teeth adapted to cut bone. Thecutting structure may have side walls having teeth adapted to cut bone.

In other embodiments, the base member may include a plurality ofperipheral anchors each positioned radially outwardly of the centralanchor and extending distally from the bone-engaging surface of thecollar a second distance to a peripheral tip, in which the firstdistance is greater than the second distance. The at least one chiselslot may be positioned between a first peripheral anchor and the centralanchor. The plurality of ribs may include four ribs, each rib positionedat an angle of about ninety degrees relative to an adjacent rib. Thefour ribs together may define four quadrants of the collar. The at leastone chisel slot may include four chisel slots, each of the four chiselslots being positioned in a corresponding one of the four quadrants ofthe collar. A first pair of ribs may be substantially parallel with eachother and extend a first total distance across the collar, and a secondpair of ribs may be substantially parallel with each other and extend asecond total distance across the collar, the second total distance beinggreater than the first total distance. The first pair of ribs may besubstantially perpendicular to the second pairs of ribs. The at leastone chisel slot may be asymmetric about at least two planes. At least aportion of the central anchor may include a bone ingrowth coating. Thecoating may extend between about 40% and about 50% of the first distanceof the central anchor. The chisel slot may be positioned along a paththat tracks adjacent to a first rib and a second rib of the plurality ofribs, the first and second ribs being circumferentially adjacent oneanother. The first and second ribs may be substantially perpendicular toeach other.

In still another aspect of the present disclosure, a base member of astemless shoulder implant includes a proximal collar having a proximalsurface and a bone-engaging surface opposite the proximal surface, acentral anchor extending distally along a longitudinal axis of the basemember from the bone-engaging surface to a distal tip. The centralanchor includes a plurality of ribs. The base member includes at leastone chisel slot extending from the bone-engaging surface to the proximalsurface and extending between two adjacent ribs of the plurality ofribs. The base member may include a plurality of peripheral anchors eachpositioned radially outwardly of the central anchor and extendingdistally from the bone-engaging surface of the collar a second distanceto a peripheral tip, the first distance being greater than the seconddistance. The plurality of ribs of the central anchor may include fourribs, each rib positioned at an angle of about ninety degrees relativeto an adjacent rib, the four ribs together defining four quadrants ofthe collar. The at least one chisel slot may include four chisel slots,each of the four chisel slots being positioned in a corresponding one ofthe four quadrants of the collar. The at least one chisel slot may beasymmetric about at least two planes. Each rib may include outer surfacehaving a width, the width decreasing in a proximal to distal direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a base of a shoulder implantaccording to a first aspect of the disclosure;

FIG. 2 is a bottom perspective view of the base of FIG. 1 ;

FIG. 3 is a top view of the base of FIG. 1 ;

FIG. 4 is a side view of the base of FIG. 1 ;

FIG. 5 is a bottom view of the base of FIG. 1 ;

FIG. 6 is a side perspective view of a base of a shoulder implantaccording to a second aspect of the disclosure;

FIG. 7 is a top perspective view of the base of FIG. 6 ;

FIG. 8 is another side perspective view of the base of FIG. 6 ;

FIG. 9 is a bottom view of the base of FIG. 6 ;

FIG. 10 is a top perspective view of an embodiment according to anotheraspect of the disclosure;

FIG. 11 is a top view of the base of FIG. 10 ;

FIG. 12 is a side perspective view of the base of FIG. 10 ;

FIG. 13 is a side view of the base of FIG. 10 ;

FIG. 14 is a top perspective view of a base of a shoulder implantaccording to another aspect of the disclosure;

FIG. 15 is a bottom perspective view of the base of FIG. 14 ;

FIG. 16 is a side view of the base of FIG. 14 ;

FIG. 17 is a bottom perspective view of the base of FIG. 14 with a nutassembled thereto;

FIG. 18 is a top perspective view of the nut of the base of FIG. 14 ;

FIG. 19 is a top perspective view of an alternate embodiment of the baseof FIG. 14 ;

FIG. 20 is a top perspective view of a base of a shoulder implantaccording to another aspect of the disclosure;

FIG. 21 is a bottom perspective view of the base of FIG. 20 ;

FIG. 22 is a cutaway view of the base of FIG. 20 implanted on a proximalhumerus; and

FIG. 23 is a schematic representation comparing an implant profile ofthe base of FIG. 20 to an implant profile of a tapered stem in aproximal humerus.

FIG. 24 is a side perspective view of a base of a shoulder implantaccording to another aspect of the disclosure;

FIGS. 25-26 are the same bottom views of the base of FIG. 24 , with thetwo figures identifying different features of the base;

FIG. 27 is a top view of the base of FIG. 24 ;

FIG. 28 is a schematic representation of the base of FIG. 24 implantedin a humerus;

FIG. 29 is a bottom perspective view of a base of a shoulder implantaccording to another aspect of the disclosure;

FIG. 30 is a side perspective view of a base of a shoulder implantaccording to another aspect of the disclosure;

FIG. 31 is a side perspective view of a chisel tool according to anotheraspect of the present disclosure;

FIG. 32 is an enlarged front perspective view of a cutting structure ofthe chisel tool of FIG. 31 ;

FIG. 33 is a side perspective view of the chisel tool of FIG. 31 inconjunction with the base of FIG. 24 ;

FIG. 34 is a side perspective view of a chisel tool according to anotheraspect of the present disclosure;

FIG. 35 is an enlarged side perspective view of a cutting structure ofthe chisel tool of FIG. 34 ;

FIG. 36 is an enlarged top view of the chisel tool of FIG. 34 inconjunction with the base of FIG. 24 ;

FIGS. 37-38 are side perspective views of the chisel tool of FIG. 34 inconjunction with the base of FIG. 24 ;

FIG. 39 is a top perspective view of a chisel tool according to anotheraspect of the disclosure in conjunction with the base of FIG. 29 ;

FIG. 40 is a bottom perspective view of a shoulder implant according toanother aspect of the present disclosure;

FIG. 41 is a bottom view of the base of FIG. 40 ;

FIG. 42 is a side view of the base of FIG. 40 ;

FIG. 43 is a front view of the base of FIG. 40 ;

FIGS. 44-45 are side views of an alternative embodiment of the base ofFIG. 40 ;

FIG. 46 is a cross-sectional view showing the surfaces of the base ofFIGS. 44-45 ; and

FIG. 47 is a side view of another alternative embodiment of the base ofFIG. 40 .

DETAILED DESCRIPTION

It should be understood that although the term “stemless implant” isused herein, the term does not indicate that a stemless implant fullylacks any anchor, but rather a stemless implant may include an anchorthat is significantly smaller and/or shorter than stems of typical knownstemmed implants. Further, the stemless implants of the presentdisclosure generally include a base member intended for coupling to anend of a first bone of a joint, such as a humerus or femur, and anarticulating member intended to attach to the base member and to providearticulation with the second bone of the joint (or a correspondingprosthesis attached to the second bone). Further, as used herein, theterm “proximal” refers to a location closer to an individual's heart,and the term “distal” refers to a location farther away from theindividual's heart. When used in the context of an implant, the terms“proximal” and “distal” refer to locations on the implant closer to, orfarther away from, the heart when the implant is implanted in anintended manner.

FIGS. 1 and 2 show a base 100 of a stemless implant according to a firstaspect of the disclosure. Base 100 generally includes collar 101 andcentral anchor 140 coupled thereto. Collar 101 may be generallycylindrical or annular and includes a proximal end surface 102, a distalbone-engaging surface 103, and side flange surface 104 extending alongthe circumference of the collar. As shown in FIG. 1 , proximal endsurface 102 may be flat, but it can also be inclined or sloped in someembodiments. As in FIG. 1 , side flange surface 104 may have a uniformheight, measured from distal to proximal ends of side flange surface104, or the height may be varied along proximal surface 102. Althoughshown as generally cylindrical or annular, collar 101 may have othershapes. Anchor 140 is coupled to collar 101 at a first end 141 andextends distally from the collar along a longitudinal axis 135 to asecond end 174. In the illustrated embodiment, anchor 140 is taperedalong longitudinal axis 135 so that first end 141 has a relatively largediameter, with the diameter of the anchor generally narrowing towardsecond end 174 until the anchor terminates in distal tip 175; however,in some situations it may be appropriate for anchor 140 to be of uniformsize throughout and not tapered. Anchor 140 further includes outer wall142 extending from first end 141 toward distal tip 175.

As shown in FIGS. 1 and 3 , base 100 includes an annular rim 119positioned within an interior cavity of collar 101. Rim 119 defines anopening 130 which is adapted to receive an articulating component (notshown) of the stemless implant. In the illustrated example, base 100 maybe adapted to couple to a proximal humerus of a patient, with aprosthetic humeral head adapted to couple to the base via opening 130,the prosthetic humeral head intended to articulate with a native orprosthetic glenoid of the shoulder joint. Although rim 119 and opening130 may have any shape that suitably mates with the correspondingportion of the prosthetic humeral head, in one example a taper such as aMorse taper may be used to lock the prosthetic humeral head to rim 119.The proximal end of rim 119 may be substantially flush with the proximalsurface 102 of collar 101, although in some embodiments it may extendeither proximally or distally of proximal surface 102. In theillustrated embodiment, the opening 130 defined by rim 119 extends fromproximal end surface 102 of collar 101 along longitudinal axis 135 to aproximal surface 139 of anchor 140. From surface 139 to tip 175, anchor140 may be generally solid, with the exceptions noted below inconnection with the flexible portions of outer wall 142.

The space between the inner circumference of collar 101 and the outercircumference of rim 119 defines a circular or cylindrical recess 115.Recess 115 extends from proximal surface 102 distally along longitudinalaxis 135 to surface 139. Rim 119 separates opening 130 and recess 115.Prior to attaching a prosthetic humeral head to base 100, or afterremoving a prosthetic humeral head from the base, tools such asinsertion and extraction tools may be inserted into opening 130 and/orrecess 115, as discussed below.

FIG. 4 shows a side view of base 100, including outer wall 142 of anchor140. As can be seen more clearly in FIG. 4 , outer wall 142 may have aserrated configuration in which the outer wall includes alternatingpeaks 143 and troughs 144 in the proximal-to-distal direction, with eachpeak transitioning into a trough and each trough transitioning into apeak. As shown in FIG. 4 , peaks 143 and troughs 144 may be disposedsubstantially circularly around outer wall 142, with the outer surfacesof the peaks and the troughs together defining the outer wall. In otherembodiments, peaks 143 and troughs 144 may be disposed helically aroundouter wall 142 in a screw-like configuration. As noted above, eachtrough 144 is positioned adjacent to at least one peak 143, andpreferably two peaks. Each peak 143 may extend farther radially outwardfrom the longitudinal axis 135 than each adjacent trough 144. Thetransition between the outer circumference of each peak 143 to adistally adjacent trough 143 forms a distal surface 147 that is shapedfrustoconically.

Although the outer circumferential surface of each peak 143 may beangled along the general contour of anchor 140, each peak may alsoinclude a generally curved surface, where a peak transitions into anadjacent trough 144. With this configuration, the proximal surface ofeach peak forms a counter support to resist pull-out, torque out, and/orlever out of the base 100 after implantation. For example, in theillustrated embodiment, the transition between the outer circumferenceof each peak 143 to a proximally adjacent trough 144 forms a hook 143 a.Hook 143 a may extend radially outwardly from adjacent troughs 144 in aproximal-facing hook shape. Hooks 143 a can be advanced into the nativebone to fix the anchor to the bone. Once hooks 143 a are engaged in thebone, motion is restricted due to the hooked shape of hooks 143 a.

FIG. 4 further illustrates a plurality of slots 160 formed in the outerwall 142 of anchor 140. Slots 160 are designed to enable flexibleportions 165 of outer wall 142 to flex and extend radially outwardly ofstatic portions 166. Each slot 160 may extend through outer wall 142 sothat the slot fully extends from the outer surface of the anchor andinto recess 115. Although various methods may be used to create slots160, in the illustrated embodiment the slot extends from holes 161 and162 distally to a bottom surface 165 of the slot. Bottom surface 165 mayextend around a portion of a circumference of anchor 140 and may bepositioned in a plane that is parallel to proximal surface 102 of collar101 and is coextensive with a plane defined by surface 139. Holes 161and 162 may be positioned on proximal portions of outer wall 142 nearfirst end 141. Holes 161 and 162 may be adjacent to each other but donot overlap, such that a thin connection is maintained between flexibleportion 165 and the remainder of outer wall 142. Although the bottomsurface 165 of slot 160 is shown as being disposed through outer wall142 at an angle generally perpendicular to longitudinal axis 135, theangle may be of varying degrees. As shown in FIG. 5 , base 100 mayinclude four slots 160 that form four flexible portions 165 positionedat substantially equal intervals around the circumference of anchor 140,but it should be understood that more or fewer slots and/or flexibleportions may be provided as desired.

Each flexible portion 165, which may be thought of as the portions ofouter wall 142 within a particular slot 160, may be biased outwardlyfrom adjacent surfaces of static portion 166 so that, in the absence ofapplied force, portions of each flexible member extend farther radiallyoutward from longitudinal axis 135 compared to circumferentiallyadjacent areas of static portion 166. With this configuration, a toolmay be used to pull the flexible portions 165 radially inward togenerally align with static portion 166 upon either insertion of base100 into bone, or extraction of the base out of bone, such that theouter wall 142 of anchor 140 forms a substantially smooth surface. Forexample, an insertion and/or extraction tool (not shown) may be insertedinto opening 130 and/or recess 115 to engage each flexible portion 165to pull the flexible portions radially inward. This constrained orcontracted condition may be referred to as the insertion and/or removalcondition. During implantation of base 100, for example into cancellousbone in a prepared proximal humerus, anchor 140 may be driven into thecancellous bone until collar 101 is substantially flush with theproximal humerus. Using a tool to transition base 100 to the insertioncondition prior to implantation may provide a substantially smoothsurface of the outer wall 142 of anchor 140 to ease the insertion of thebase into the bone. Once base 100 is in the desired position in theproximal humerus, the tool may be disengaged from base 100, allowingflexible portions 165 to flex radially outwardly into the bone in whichthe base is implanted. This condition may be referred to as theimplanted or expanded condition. This additional radial force mayfurther aid in achieving suitable fixation of the base 100, despite thebase being stemless. Further, during a revision procedure in which base100 must be removed from the bone, merely pulling the base proximallyout of the bone risks trauma due to the flexible portions 165. Thus, atool similar or identical to that described above may again be insertedinto opening 130 and/or recess 115 and engage each of the flexibleportions 165 to move them radially inwardly into the removal condition.This transition helps to create clearance between the proximal humerusand the outer wall 142 of anchor 140, particularly at the locations ofthe flexible portions 165. In some embodiments, in the absence ofapplied force, the flexible portions 165 may extend less than about 2 mmor about 3 mm compared to circumferentially aligned areas of staticportion 166. Although this amount of extension may seem small, theradial extension may enable the hooks 143 a associated with the flexibleportions 165 to further engage the bone for increased fixation. Itshould also be understood that the tool used to transition the base fromthe insertion condition or removal condition to the implanted orexpanded condition may be the same tool that is used to hold the base100 during implantation or explantation, although it may also be aseparate tool with no additional function.

FIGS. 6 and 7 show a base 200 of a stemless implant according to asecond embodiment of the disclosure. Base 200 generally includes collar201 coupled with central anchor 240. Collar 201 may be generallycylindrical or annular and includes a proximal end surface 202, a distalbone engaging-surface 203, and a side flange surface 204. Proximal endsurface 202 may be flat as shown, but in other embodiments it may beinclined or sloped. Side flange surface 204 may have a uniform height,the height measured from distal to proximal ends of side flange surface204, or the height may vary along proximal end surface 202. Althoughshown as generally cylindrical or annular, collar 201 may have othershapes.

Base 200 includes central anchor 240 coupled to collar 201 at a firstend 241 and extending distally from the collar along a longitudinal axis235 to a second end 274. In the illustrated embodiment, anchor 240 istapered along longitudinal axis 235 so that first end 241 has arelatively large diameter, with the diameter of the anchor generallynarrowing toward second end 274 until the anchor terminates in distaltip 275; although, in some situations it may be appropriate for, anchor240 to be of uniform size throughout and not tapered.

When used as part of a shoulder implant system, anchor 240 may beconfigured to be driven into the metaphyseal cancellous bone of thehumerus and to facilitate engagement between base 200 and the bone forfixation. Anchor 240 may include a plurality of flutes 255 which mayextend part or all of the longitudinal length of the anchor, for examplefrom bone-engaging surface 203 to distal tip 275. Each flute 255 may bepositioned between two edges 257, with the flute being recessed radiallyinwardly toward longitudinal axis 235 compared to the edges. Edges 257may extend radially outwardly from longitudinal axis 235 to varyingdegrees depending on the position along the longitudinal axis. Forexample, edges 257 may have a minimum amount of radial extension fromlongitudinal axis 235 at or near distal tip 275. The distance which theedges 257 extend radially outwardly from longitudinal axis 235 may thenincrease gradually in the proximal direction toward bone-engagingsurface 203. The edges 257 may reach their greatest amount of outwardradial extension from longitudinal axis 235 at apex 258. From apex 258to bone-engaging surface 203, the distance which edges 257 extendradially outward from longitudinal axis 235 may decrease until the edgesconnect to bone-engaging surface 203. Flutes 255 are preferably concavebetween two adjacent edges 257. Each flute 255 may include an enhancedfixation surface 259 in the region between bone-engaging surface 203 anda portion of the flute circumferentially aligned with apex 258. Theenhanced fixation surface 259 may take the form of a porous metalsurface, such as porous titanium alloy, including Tritanium® byHowmedica Osteonics Corporation. As shown in FIG. 8 , fixation surface259 may be in the general shape of a trough and may be convex. Fixationsurfaces 259 may provide for enhanced in-growth of bone into anchor 240,facilitating better fixation of base 200 following implantation.Fixation surfaces 259 may be rougher than the adjacent surfaces ofanchor 240, resulting in greater friction between the fixation surface259 and the bone. This increased friction may help provide additionalfixation by providing additional resistance against pull-out forces.

A fixation ring 238 may surround central anchor 240, the fixation ringextending circumferentially around the central anchor at its connectionwith bone-engaging surface 203. Fixation ring 238 may generally take theform of a recessed groove. As explained in greater detail below, uponimplantation of base 200 into cancellous bone, the bone may flow intofixation ring 238 to help provide additional fixation. As shown in FIG.7 , fixation surfaces 259 may extend into portions of fixation ring 238to provide stronger fixation to the bone.

When implanting base 200 into a bone, such as the cancellous bone at theproximal end of the humerus, distal tip 275 of anchor 240 is driven intothe bone. Because cancellous bone is relatively soft, the bone mayeffectively flow along anchor 240, and in particular along the flutes255 of the anchor. After the apex 258 of the edges 257 passes into thebone, some volume of bone may effectively “spring” back into the areasof flute 255 adjacent enhanced fixation surfaces 259 and also intofixation ring 238. The positioning of the fixation ring 238 in the areaof the flutes 255 proximal to the apex 258 results in stronger pull-outresistance for base 200, with the resistance increasing further as bonegrows into the pores of fixation surface 259 and fixation ring 238.

As shown in FIGS. 8 and 9 , collar 201 defines a plurality of holes 211and 213 extending from proximal end surface 202 to bone-engaging surface203 and includes a plurality of peripheral anchors or pegs 210 extendingdistally from bone-engaging surface 203 to distal tips 220. Pegs 210 aidin the fixation of base 200 to the bone, and may particularly assist ininitial fixation. While there can be any number of pegs 210 on collar201, preferably there are four pegs positioned at substantially equalcircumferential intervals around the collar. As shown best in FIG. 9 ,pegs 210 may be located radially outward of holes 213, although otherrelative spacing between pegs 210 and holes 213 may be appropriate. Theuse of at least four pegs 210 may provide for enhanced feedback,especially compared to the use of three or fewer pegs, while seatingbase 200 into the prepared bone during insertion. For example, uponinitial contact of pegs 210 with a prepared flat bone surface, thesurgeon may be able to easily determine if each of the pegs issimultaneously in contact with the bone. In particular, if all four pegs210 are in contact with the proximal surface of the bone, the base 200should not experience any significant amount of rocking or tilting. Ifthe surgeon notices rocking of the base 200, it should be clear that allfour pegs 210 are not simultaneously in contact with the bone. If base200 included three pegs, on the other hand, this rocking motion wouldnot be expected despite a mismatch between a plane defined by the tipsof the pegs and a plane of the prepared proximal bone.

As shown in FIG. 8 , pegs 210 extend distally from bone-engaging surface203 to distal tips 220. Pegs 210 may also include flutes 215. Each flute215 is positioned between two edges 217, and flutes 215 may be generallyconcave between the two edges 217. Each peg 210 may have a substantiallyidentical structure to central anchor 240 but scaled to a smaller size.Those structures may provide substantially the same effect as thecorresponding features on central anchor 240, although the effects maybe less dramatic due to the smaller sizes of the pegs compared to thecentral anchor. However, in other embodiments, the pegs 210 do not needto have identical but scaled down features as the central anchor 240.

As shown in FIGS. 7-9 , holes 211 and 213 extend from proximal surface202 to bone-engaging surface 203. Holes 211 and 213 may be in any shape,round, oval, oblong, etc. Alternatively, holes 211 may be openingsextending from proximal surface 202 to bone-engaging surface 203 nearside wall 204, such that side wall 204 includes curved recesses in theside wall. In the illustrated embodiment, holes 211 are oblong and amajor axis of each hole extends from a point near central anchor 240radially outwardly toward a point near side flange 204 of collar 201.Holes 213, may also be oblong, and slightly curved so that a major axisof each hole extends in the circumferential direction around centralanchor 240. Holes 211 and 213 may have various uses. For example, holes211 and 213 may be used for passing one or more sutures through to aidin fixation of an object to the base 200. Still further, holes 211 and213 may be used to engage insertion and/or extraction instrumentation.In the illustrated embodiment, there are four holes 211 and four holes213, but there may be more or fewer of each of hole 211 and 213.Further, there is no requirement that the number of holes 211 equal thenumber of holes 213.

In addition to the uses described above, holes 213 may be sized andpositioned to facilitate a revision procedure after the base 200 hasbeen implanted into a patient for an amount of time. In the embodimentillustrated in FIG. 8 , holes 213 are positioned adjacent fixationsurfaces 259 of flutes 255 and fixation ring 238. With this positioningof holes 213, a surgeon may insert a tool through holes 213 in order tochisel, ream, or otherwise cut away at bone that is adjacent to fixationsurface 259 and/or fixation ring 238. Strategically cutting away theseareas of bone allows for easier removal of base 200 so that a new devicemay be implanted in its place.

Each hole 211 may be spaced generally midway between two adjacent pegs210. However, in some embodiments each hole 211 may be positionedadjacent a corresponding peg 210. In such an embodiment, each hole 211is preferably disposed adjacent a same side of the associated peg 210.In other words, each hole 211 may be disposed on the right side adjacentto each peg 210, or each hole 211 may be disposed on the left sideadjacent to each peg. With each hole 211 adjacent the same side of anassociated peg 210, a tool inserted through the holes 211 may be used toream or cut bone adjacent pegs 210, such that the base 200 may berotated to move the pegs into the bone cavity adjacent the holes 211.This process may allow for easier removal of base 200 during a revisionsurgery. Rather than having one hole associated with each peg 210, eachpeg may include two holes on either side of the peg so that the base 200may be rotated in either direction to facilitate extraction of the base.

As with base 100, base 200 may further define an opening 230. Opening230 may extend distally along longitudinal axis 235 from proximalsurface 202 of collar 201. Opening 230 may extend partially or fullythrough anchor 240 along longitudinal axis 235 or it may be shallow andextend only into collar 201. A humeral head component (not shown) may beplaced within opening 230 and attached thereto, for example by a taperlock such as a Morse taper. The humeral head component may be attachedby any known securement means including screw or friction fit.

It should be understood that bases 100 and 200 may be formed of anysuitable prosthetic grade material, including, for example, titaniumalloys and/or other biocompatible metals and metal alloys. In someembodiments of base 200, the porous portions of the base, such asfixation surface 259 and fixation ring 238, may be provided via additivemanufacturing over a base material such as titanium alloy. Further,although holes 211 and 213 are only described in connection with base200, similar or identical holes may be provided in base 100. Stillfurther, base 100 may include surfaces similar to fixation surfaces 259and fixation ring 238, for substantially the same purpose of increasedfixation.

FIGS. 10-13 show base 300 of a stemless implant according to anotheraspect of the disclosure. Base 300 generally includes collar 301 coupledwith central anchor 340. Collar 301 may be generally cylindrical orannular and includes a proximal end surface 302, a distal boneengaging-surface 303, and a side flange surface 304. Proximal endsurface 302 may be flat as shown, but in other embodiments it may beinclined or sloped. Side flange surface 304 may have a uniform height,the height measured from distal to proximal ends of side flange surface304, or the height may vary along proximal end surface 302. Althoughshown as generally cylindrical or annular, collar 301 may have othershapes.

Base 300 includes central anchor 340 coupled to collar 301 at a firstend 341 and extending distally from the collar along a longitudinal axis335 to a second end 374. In the illustrated embodiment, anchor 340 isslightly tapered along longitudinal axis 335 so that first end 341 has arelatively larger diameter, with the diameter of the anchor slightlynarrowing toward second end 374; although, in some embodiments, anchor340 may be of uniform size and not tapered.

As shown in FIGS. 10 and 11 , base 300 includes a socket, which in theillustrated embodiment is a hex member 319, positioned within aninterior cavity of collar 301. Hex member 319 defines an opening 330which is adapted to receive an articulating component (not shown) of thestemless implant. In the illustrated embodiment, opening 330 extendsfrom proximal end surface 302 of collar 301 along longitudinal axis 335to annular proximal surface 339 of anchor 340, where the diameter of theopening decreases. With the decreased diameter, opening 330 then extendsfrom annular proximal surface 339 of anchor 340 along longitudinal axis335 to second end 374. Thus, anchor 340 of base 300 may be cannulated.In this way, base 300 may be inserted through a pilot wire, such as aK-wire, to help provide more accurate placement of base member 300within a prepared portion of the bone. As illustrated, hex member 319has a hexagonal shape. The proximal end of hex member 319 may besubstantially flush with the proximal surface 302 of collar 301,although in some embodiments it may extend either proximally or distallyof proximal surface 302. A driver (not shown) having a mating internalhex member may engage hex member 319. This may cause rotation of hexmember 319 and base 300 which may provide torque for fixation of basemember 300 in the bone. It should be understood that although the socketis illustrated as having a hexagonal shape, any shape suitable fortransmitting torque from a correspondingly shaped driver tool may besuitable.

Anchor 340 includes outer wall 342 extending from first end 341 towardsecond end 374. When used as part of a shoulder implant system, anchor340 may be configured to be driven into the metaphyseal cancellous boneof the humerus and to facilitate engagement between base 300 and thebone for fixation. Threads 345 extend around outer wall 342 of anchor340 and may be disposed helically in a screw-like configuration. Whenthe driver (not shown) engages hex member 319 and causes rotation ofbase 300, threads 345 may engage the bone and may provide greaterfixation of the base to the bone.

FIGS. 14-17 show base 400 of a stemless implant according to anotheraspect of the disclosure. Base 400 generally includes collar 401 coupledwith central anchor 440. Collar 401 may be generally cylindrical orannular and includes a proximal end surface 402, a distal boneengaging-surface 403, and a side flange surface 404. Proximal endsurface 402 may be flat as shown, but in other embodiments it may beinclined or sloped. Side flange surface 404 may have a uniform height,the height measured from distal to proximal ends of side flange surface404, or the height may vary along proximal end surface 402. Collar 401may have other shapes, such as generally oblong and may includeadditional holes for use with insertion/extraction tools and/or foraccepting sutures, similar to holes described in embodiments above.

Base 400 includes central anchor 440 coupled to collar 401 at a firstend 441 and extending distally from the collar along a longitudinal axis435 to a second end 474. As illustrated, anchor 440 may include flanges451 extending from bone-engaging surface 403, substantially parallel tolongitudinal axis 435, to second end 474 of the anchor. As shown inFIGS. 15 and 16 , flanges 451 may include outer surfaces 452 and innersurfaces 453. Inner surfaces 453 may be slightly concave along at leasta portion of the inner surfaces. Inner surfaces 453 may include internalthreads along at least a portion thereof. Flanges 451 may include astraight portion 480 and a tapered portion 481. Straight portion 480 mayextend generally parallel to longitudinal axis 435, whereas taperedportion 481 may taper radially inwardly from the distal end of straightportion 480 to second end 474 of anchor 440 such that inner surfaces 453nearer second end 474 may be radially closer to longitudinal axis 435than a point on inner surface nearer straight portion 480. Likewise,outer surfaces 452 nearer second end 474 may be radially closer tolongitudinal axis 435 than a point on the outer surface nearer straightportion 480. However, the degree of the taper of the outer surfaces 452and inner surfaces 453 of flanges 451 may be different. For example, thetaper of outer surfaces 452 may be less than the taper of the innersurfaces.

Anchor 440 includes support 472, which may be a cylinder, extending frombone-engaging surface 403 of collar 401 along longitudinal axis 435 to adistal end surface 471 of the cylinder. Support 472 may be positionedgenerally centrally on bone-engaging surface 403.

Base 400 includes opening 430 extending from proximal end surface 402 ofcollar 401 along longitudinal axis 435 to a distal end surface 471 ofsupport 472. The diameter of opening 430 may decrease near the distalend of support 472. In the illustrated example, base 400 may be adaptedto couple to a proximal humerus of a patient, with a prosthetic humeralhead adapted to couple to the base via opening 430, the prosthetichumeral head intended to articulate with a native or prosthetic glenoidof the shoulder joint. Although opening 430 may have any shape thatsuitably mates with the corresponding portion of the prosthetic humeralhead, in one example a taper such as a Morse taper may be used to lockthe prosthetic humeral head within opening 430.

As shown in FIGS. 17 and 18 , anchor 440 may include screw nut 450. Nut450 may include a proximal end surface 456, a side flange surface 457,an angled surface 458, and a distal end surface 459. Nut 450 may begenerally cylindrical. In the illustrated embodiment, nut 450 includesangle surface 458; however, in other embodiments side flange surface 457may connect with proximal end surface 456 and there may not be an angledsurface. Nut 450 may include two openings 470 extending alonglongitudinal axis 435 from respective proximal and distal end surfaces456 and 459. Openings 470 may not connect and may remain two distinctopenings. Openings 470 may have a hexagonal shape to matingly engagewith a driver for rotation of the nut and movement in a distaldirection, although any shape for transmitting torque from acorrespondingly shaped driver may be suitable. Distal opening 470 may beused for manufacturing assembly. A tool (not shown) may couple withdistal opening 470 to insert nut 450 into anchor 440. Nut 450 mayinclude external threads on the outer circumference of side flangesurface 457. The threads may be adapted to matingly engage the threadson inner surfaces 453 of flanges 451. Nut 450 may maintain contact withat least a portion of inner surfaces 453 of the flanges.

Flanges 451 of anchor 440 may be expandable. The diameter of nut 450across side flange surface 457 may be greater than the diameter acrossthe inner surfaces 453 of tapered portion 481 of the flanges. During animplantation procedure, base 400 may be implanted into a bone, such as aproximal humerus, with nut 450 positioned in contact with or adjacent tosupport 472. In this position, flanges 451 are in an insertion condition(which may also be referred to as a removal condition) in which thediameter of anchor 440 is in a constrained or contracted condition.After implanting anchor 440 into the proximal humerus, for example incancellous bone, a driver may be passed through opening 430, with an endof the driver engaging the opening 470 of nut 450. The surgeon maymanually or otherwise rotate the driver to cause corresponding rotationof nut 450, while the remainder of base 400 remains stationary withrespect to the bone. Rotation of nut 450 results in external threads ofthe nut engaging internal threads of the flanges 451 so that the nuttranslates distally toward tapered portion 481 of flanges 451. As thenut 450 is driven distally, it engages tapered portion 481 of flanges451. Because the nut 450 has a larger diameter than the internaldiameter of flange 451 when the flanges 451 are in the implantedcondition, the nut forces the flanges to expand outwardly into anexpanded or implanted condition. This expansion of flanges 451 into thecancellous bone may provide for enhanced fixation between base 400 andthe bone, for example by increasing the force required for the base tobe pulled out of the bone.

At least one flange 451 may include a stop (not shown) near the distalend of the flanges. The stop is designed to limit the distance nut 450can translate distally. In another example, a driver (not shown) havinga positive stop may be used to translate the nut while preventingtranslation beyond the intended position. The driver may be used aloneor in conjunction with a stop on the flanges. In this way, the nut 450will translate distally only to an intended location.

FIG. 19 illustrates base 400′ that is identical to base 400 in mostrespects. For example, anchor 440′ of base 400′ may be completelyidentical to anchor 440, and may include a screw nut identical to screwnut 450. Thus, those components are not described again. However, collar401′ of base 400′ may have an alternate shape. Whereas collar 401 ofbase 400 is illustrated as being cylindrical, collar 401′ may be oblongwith two substantially straight portions on the anterior and posteriorsides of the collar, with two substantially rounded portions on themedial and lateral sides of the collar. The width of collar between theanterior and posterior ends may gradually increase from the medialrounded portion toward the lateral rounded portion, which may bettercorrespond to the native anatomy of the proximal humerus. In addition toopening 430′, which may be identical in form and function to opening430, collar 401′ may include additional openings 431′ that may be usedto mate with an insertion or extraction tool (not shown) or for othersuitable purposes, such as for receiving sutures, etc.

It should be understood that bases 300 and 400 may be formed of anysuitable surgical grade material, including, for example, titaniumalloys and/or other biocompatible metals, metal alloys, and/or plastics.Further, although holes 211 and 213 are only described in connectionwith base 200, similar or identical holes may be provided in bases 300and 400 for similar purposes.

For each base described above, if being used in a shoulder jointapplication for coupling to a prosthetic humeral head, the proximalhumerus is generally prepared to have a substantially planar surfaceprior to implantation of the base. As noted earlier, each base describedherein may be referred to as a stemless base. The collar of each base,however, may have a perimeter that is substantially similar to, or fitswithin, the perimeter of the proximal end of a typical stemmed base (notshown) for a more traditional shoulder implant. With this configuration,if a surgeon begins preparing a patient's proximal humerus to accept anyof the bases described herein, and it is determined that a stemlessimplant will ultimately not be suitable for use in the patient, thesurgeon may instead use a traditional stem in the patient, even thoughthe proximal humerus was prepared for a stemless implant. In otherwords, the geometries of the bases described herein, and in particularthe collars of the bases, allow a surgeon a contingency plan ofswitching to a traditional stemmed shoulder implant mid-procedure, ifsuch a contingency plan is deemed preferable and/or necessary.

FIGS. 20-23 show base 500 of a stemless implant according to anotheraspect of the disclosure. Base 500 generally includes collar 501 coupledwith central anchor 540. Collar 501 may have a generally roundedcruciform shape, although in other examples, the collar may have othershapes including oblong or annular. Collar 501 includes a proximal endsurface 502, a distal bone engaging-surface 503, and a side flangesurface 504. Proximal end surface 502 may be flat as shown, but in otherembodiments it may be inclined or sloped. Side flange surface 504 mayhave a uniform height, the height measured from distal to proximal endsof side flange surface 504, or the height may vary along proximal endsurface 502. Distal bone-engaging surface 503 may include a poroussurface, for example porous titanium alloy, across all or a portion ofits surface to provide better fixation of the implanted base with thebone.

Collar 501 includes at least one hole 525 extending from proximal endsurface 502 to distal bone-engaging surface 503. The holes 525 are eachadapted to receive a screw. In the illustrated embodiment, there arefour holes 525 and four screws, although there can be more or fewerholes and/or screws. The screws may be variable angle locking screwscapable of being inserted through holes 525 at variable angles, with theheads of the screws having locking threads to mate with correspondinglocking threads in the holes. The screws may engage the bone to providefixation of base 500 in the bone. As shown in FIGS. 21-23 , the screwsmay have varying lengths to accommodate bone purchase to help withfixation, although any combination of screw lengths may be appropriate.In the illustrated embodiment, the medial screw has a length that isgreater than the length of central anchor 540.

Base 500 includes central anchor 540 coupled to collar 501 at a firstend 541 and extending distally from the collar along a longitudinal axis535 to a second end 574. In the illustrated embodiment, anchor 540 has astraight portion 536, which may be cylindrical, and a tapered portion537, which may be conical or frustoconical. Tapered portion 537 istapered along longitudinal axis 535 so that the proximal end of thetapered portion has a relatively large diameter, with the diameter ofthe anchor generally narrowing toward second end 574 until the anchorterminates in distal tip 575.

As with previous embodiments of the bases, base 500 may further definean opening 530. Opening 530 may extend distally along longitudinal axis535 from proximal surface 502 of collar 501. Opening 530 may extendpartially or fully through anchor 540 along longitudinal axis 535 or itmay be shallow and extend only into collar 501. A humeral head component(not shown) may be placed within opening 530 and attached thereto, forexample by a taper lock such as a Morse taper. The humeral headcomponent may be attached by any known securement means including screwor friction fit. Base 500 may include additional holes for use withinsertion/extraction tools and/or for accepting sutures, similar toholes described in embodiments above.

FIG. 22 shows base 500 implanted within a humeral bone with variableangle locking screws. The benefit of using screws of different lengthsis particularly well illustrated in FIG. 22 . For example, a screw thatengages a hole 525 on the medial side of collar 501 may be longer thanthe other screws, as there may be a greater depth of bone available inthis area.

FIG. 23 illustrates base 500 implanted into a humeral bone, similar toFIG. 22 . However, FIG. 23 also illustrates the expected implant profileof a traditional stem 590 of a stemmed shoulder implant. As can be seenby the superimposition of base 500 with the profile of a traditionalstem 590, the base 500 may be designed so that much or all of theportion of the base implanted into the humerus would occupy space thatwould also be occupied by a traditional stem 590, if a traditional stem590 were implanted into the humerus. As a result, if a humerus isprepared to accept base 500, and it is determined that a moretraditional shoulder implant with stem 590 would be desirable, thesurgeon may choose to use traditional stem 590 instead. It should beunderstood that this concept may apply to each of the other basesdescribed herein, so that a surgeon may prepare a proximal humerus toaccept any of the bases described above or below (e.g. bases, 100, 200,300, 400, 600, 600′, 600″, 900, etc.) and may choose mid-procedure toswitch to a tapered stem 590 without having unnecessarily removed anybone. Such a change in procedure may become desirable, for example, ifthe surgeon determines that the stemless base would not be able toachieve suitable fixation with the humerus, for example because the bonequality is low.

FIGS. 24-28 show base 600 similar to bases 200 in many respects, thesimilar or identical features of which will not be described again here.In the illustrated embodiment, base 600 has a collar 601 that isgenerally annular, and may be circular, although in other examples, thebase can be any shape, such as triangular, trapezoidal, etc. Base 600includes curved side wall 604 which extends between proximal surface 602and bone-engaging surface 603. The curve of side wall 604 may help todecrease the amount of bone removed during surgery. Proximal surface 602may include opening 630 which is adapted to receive an articulatingcomponent (not shown) of the stemless implant.

Base 600 includes central anchor 640 extending distally frombone-engaging surface 603 to distal end 675. Anchor 640 includes aplurality of ribs 670, each rib projecting radially outward of distalend 675 and extending to bone-engaging surface 603. Ribs 670 extendalong bone-engaging surface 603 to a position in close proximity to oradjacent to side wall 604. Each rib 670 includes two lateral side walls671 and curved outer surface 673 between the two lateral side walls.Lateral side walls 671 may be flat, concave, and/or convex. The outersurface 673 is rounded which may provide more surface to create bonein-growth after implantation of the base 600.

Referring to FIGS. 25-26 , base 600 may include four ribs 670 that forma general “X” shape. As shown in FIG. 26 , two pairs of adjacent ribsmay be oriented about 60 degrees apart from one another, and two otherpairs of adjacent ribs may be oriented about 120 degrees apart from oneanother. However, it should be understood that other angles between thepairs of adjacent ribs may be suitable.

Anchor 640 includes surfaces 676 extending from distal end 675 tobone-engaging surface 603. In the illustrated embodiment, each surface676 is positioned between two ribs 670, although in other examples theremay be more or fewer surfaces 676. In the illustrated embodiment,surfaces 676 are rounded and include grooves or channels 677 positionednear the distal end 675 of the base and extending in a direction towardbone-engaging surface 603. Channel 677 tapers inwardly as it extends inthe direction toward distal end 675. Channel 677 may help facilitatebone in-growth after base 600 is implanted.

Base 600 may include holes 612 extending from proximal surface 602 tobone-engaging surface 603. In the illustrated embodiment, base 600includes two holes 612, each positioned between the ribs 670 that arespaced substantially 60 degrees apart from one another. In otherexamples, however, there may be more or fewer holes 612 on the base 600.Additionally, holes 612 may have the same diameter, or as in theillustrated embodiment, the holes 612 may have different diameters. Asshown in FIGS. 26-28 , superior hole 612 a has a smaller diameter thaninferior hole 612 b. Superior hole 612 a is configured to receivevariable angle screw 695, the threaded diameter of which can be fromabout 3 to about 6 millimeters (mm) and is preferably about 4.5 mmAdditionally, variable angle screw 695 can have about a 15 degreepre-tilt angle. Inferior hole 612 b is configured to receive fixed anglescrew 697, the threaded diameter of which can be from about 5 to about 7mm and is preferably about 6.5 mm Variable angle screw 695 can have alonger shaft than fixed angle screw 697. For example, variable anglescrew 695 may have a threaded shaft of about 24 mm, and fixed anglescrew may have a threaded shaft of about 20 mm.

When implanted, base 600 is preferably oriented such that superior hole612 a is positioned superior to inferior hole 612 b in relation to theshoulder. The inferior hole having a larger diameter may allow for agreater degree of fixation in the better quality bone having greaterdensity.

Base 600 includes pegs 610 extending distally from bone-engaging surface603. Pegs 610 may be shaped identically to pegs 210 of base 200. In theillustrated embodiment, there are two pairs of pegs 610 positionedradially outward of lateral side walls 671 of ribs 670. Each pair ofpegs 610 is positioned between ribs 670 that are spaced about 120degrees apart from one another. However, there may be more or fewer pegs610, which may be larger or smaller. In some examples, base 600 may notinclude any pegs.

Like base 200, base 600 may include one or more enhanced fixationsurfaces on portions of anchor 640 and bone engaging surface 603. Theenhanced fixation surface may also be positioned on portions of pegs 610and may extend onto side walls 604 of the base member. Generally, theenhanced fixation surface is positioned on proximal portions of theanchor 640 and the pegs 610. The enhanced fixation surface may beidentical to enhanced fixation surface 259 of base 200 and may take theform of a porous metal surface, such as a porous titanium alloy,including Tritanium® by Howmedica Osteonics Corporation.

Base 600 includes continuous chisel slots 613 extending throughbone-engaging surface 603 to proximal surface 602. Chisel slots 613 arepositioned near the connection of ribs 670 and surfaces 676 withbone-engaging surface 603. Thus, in the illustrated embodiment, chiselslots 613 include elongated portions 614 that track near ribs 670 andsubstantially curved portions 616 that track near surfaces 676.Elongated portions 614 may be substantially straight or may exhibit acurved shape. Each chisel slot 613 may form a substantially “M” shapewith each chisel slot including two elongated portions 614 and onecurved portion 616 in between the two elongated portions. Elongatedportions 614 track adjacent rib 670, and extend in a direction that isabout 30 degrees from a central axis C of the base that extends throughthe center of both holes 612. Each elongated portion 614 has a width W,and the curved portion 616 has a width Y, the widths W and Y may besubstantially equal or they may be different. Additionally, in analternative embodiment, the two elongated portions 614 of each chiselslot 613 may have different widths from each other.

Chisel slots 613 are sized and positioned to facilitate a revisionprocedure after base 600 has been implanted into a patient for an amountof time. In the illustrated embodiment, chisel slots 613 are positionedadjacent to pegs 610, surfaces 676 and lateral side walls 671 of theribs 670. With this positioning of chisel slots 613, a surgeon mayinsert a tool into each slot 613 in order to chisel, ream, or otherwisecut away at bone that is adjacent to pegs 610, surfaces 676, and lateralside walls 671 of the ribs 670. This strategic positioning of the chiselslots 613 allows for loosening of the bone ingrowth on enhanced fixationsurfaces, which provides for easier removal of the base 600 so that anew device may be implanted in its place. Additionally, the “M” shape ofthe chisel slots may provide more stability to a chisel tool as theshape of the chisel slot may require less bending of a correspondinglyshaped tool.

Although not shown, base 600 may include a feature similar to fixationring 238 of base 200. This fixation portion may surround all or a partof anchor 640 and may take the form of a recessed groove. The recessedgroove may include an enhanced fixation surface to provide for betterfixation of the base in bone.

FIG. 29 shows base 600′ that is similar or identical to base 600 in mostrespects, the similar features of which will not be described hereagain. Each chisel slot 613′ of the base 600′ additionally includes acentral elongated portion 614′ extending radially outward from curvedportion 616′ and positioned between a pair of adjacent pegs 610′.Central elongated portion 614′ may help during revision procedures, asfurther described below.

FIG. 30 shows base 600″ that is similar in many respects to bases 600,600′, the similar features of which will not be described again here.Base 600″ includes anchor 640″ having ribs 670″. At least one rib 670″includes fish hook serrations 672″ positioned on a portion of the curvedouter surface 673″. Serrations 672″ are sharp slots positioned on theouter surface 673″ of a rib 670″ that create better bite into the boneduring implantation of the base 600″.

FIGS. 31-33 show chisel tool 700 that can be used with bases 600, 600′,600″, particularly during a revision surgery. Chisel 700 includes handle710 at proximal portion 702, cutting structure 720 at distal portion704, and shaft 715 extending between the handle and the cuttingstructure. Cutting structure 720 has a complementary shape to chiselslot 613, such that the cutting structure is sized and configured to fitwithin the chisel slot. In the illustrated embodiment, cutting structure720 has a substantially “M” shape and includes support 722 and twoprongs 724 positioned on either side of the support. Support 722includes opposing rounded surfaces sized and configured to fit withincurved portion 616 of the chisel slot 613, one surface is generallyconvex, and the other surface is generally concave. Each prong 724includes opposing flat surfaces 726 that terminate at a distal surface726, which is a substantially straight, flat cutting edge. Although inother examples, the cutting edge may include serrations, teeth, barbs,or other cutting features. Prongs 724 are sized and configured to fitwithin elongated portions 614 of the chisel slot 613 and are offset froma longitudinal axis of the chisel. In the illustrated embodiment, prongs724 extend further distally than support 722, although in otherexamples, the support can extend the same distance as the prongs. Chiseltool 700 is designed such that cutting structure 720 can be insertedinto and through chisel slots 613 to remove bone. The positioning of thechisel slots in close proximity or adjacent to ribs 670 and pegs 610allows for removal of bone near the enhanced fixation surfaces, whichenables disengagement of the ribs and the pegs for easier removal of thebase component during a revision surgery.

FIG. 33 shows a system including chisel tool 700 in conjunction withbase 600. As illustrated, prongs 724 are inserted through elongatedportions 614 of the chisel slot 613 and support 722 is inserted incurved portion 616 of the chisel slot.

FIGS. 34-38 show another embodiment of a chisel tool 800 for use withbases 600, 600′, 600″. Chisel 800 includes handle 810 at proximalportion 802, cutting structure 820 at distal portion 804, and shaft 815extending along a longitudinal axis and terminating at distal surface817. Handle 810 can be any structure that provides a support for asurgeon to hold, and in the illustrated embodiment, the handle is a “T”bar. Handle 810 may include an impaction feature, not shown forimpacting the chisel into bone. Shaft 815 is generally cylindrical andhas a diameter D that is less than the width Y of the curved portion 616of the chisel slot 613 of the base 600, as shown in FIG. 37 . Cuttingstructure 820 extends generally transverse to the longitudinal axis ofthe shaft and includes curved portion 816 extending outwardly from adistal end of the shaft 815 and elongated portion 814 connected to thecurved portion. Cutting structure 820 is sized and configured to fitwithin chisel slot 613 of base 600, such that elongated portion 814 andcurved portion 816 each have a width that is less than the width of thechisel slot. Specifically, as shown in FIG. 36 , elongated portion 814of the cutting structure 820 of the chisel 800 has a width Z that isless than the width W of the elongated portion 614 of the chisel slot613 of the base 600. In this manner, cutting structure 820 of the chisel800 extends into and through the chisel slot 613 to remove the bonein-growth for easier removal of the base during a revision surgery.

Cutting structure 820 includes proximal surface 827, distal surface 826opposite the proximal surface, and side walls 829 extending between theproximal and distal surfaces. Proximal surface 827, distal surface 826and side walls 829 are substantially flat and may include a plurality ofcutting members or teeth 828 projecting from each surface to aid in thecutting of bone during a revision surgery. Distal surface 817 of shaft815 also includes teeth 828 projecting distally therefrom, and in someexamples, a portion of the length or the entirety of the length of shaft815 includes a cutting feature, such as teeth 828. The cutting featuresincluded on the proximal and distal surfaces and the side walls may bethe same or different. For example, the side walls may include ridges,and the distal surface may include protrusions.

During a revision surgery, chisel tool 800 is aligned with chisel slot613 of a base, for example base 600. For example, elongated portion 814of chisel tool 800 is aligned with a first elongated portion 614 of afirst chisel slot 613. A surgeon impacts handle 810 to drive cuttingstructure 820 into bone for bone removal. With cutting structure 820extended completely through chisel slot 613, torque is applied to handle810 to rotate the cutting structure to remove bone. The removal of thebone is facilitated and expedited by the sharp teeth 828 on the cuttingstructure 820. After the bone under the first chisel slot 613 isremoved, the chisel tool can be used in the same manner to remove thebone under the second chisel slot of the base.

In another embodiment, two chisel tools 800 may be used together with acenter guide (not shown) inserted within opening 630 of the base 600.The center guide may be impacted to remove the implant during revisionsurgery.

In another alternative embodiment of chisel tool 800 (not shown), thecutting structure may be symmetric about the central axis, such that thecutting structure mimics the shape of chisel slot 613, and there is anidentical curved portion and elongated portion of the cutting structureon an opposing side of the shaft. In this manner, both elongatedportions 614 of a first chisel slot 613 can be removed at the same time.

FIG. 39 shows chisel tool 800′ in conjunction with base 600′, the chiseltool 800′ is similar in most respects to chisel tool 800, the similarfeatures of which will not be described. Chisel tool 800′ has a shapecomplementary to chisel slot 613′ of base 600′. Chisel tool 800′includes cutting structure 820′ with curved portion 816′ and elongatedportion 814′ on opposing sides of shaft 815′. Cutting structure 820′also includes central elongated portion 814′ projecting from curvedportion 816′ sized and configured to fit into central elongated portion614′ of the chisel slot 613. Each of the elongated portions 614′ and thecurved portion 616′ includes a cutting feature, similar to the pluralityof teeth 828 of the chisel 800. In this manner, chisel tool 800′ canremove bone from the entirety of the chisel slot 613′ at the same time.Additionally, central elongated portion 814′ allows for greater accessto the bone between pegs 610′, which can help to remove the bone betweenthe pegs more easily to disengage the pegs. This can facilitate aneasier removal of the base 600′ during revision surgery.

FIGS. 40-43 show base 900 according to yet another aspect of the presentdisclosure. Base 900 is similar to bases 200 and 600, the similarcomponents of which will not be described again. In the illustratedembodiment, base 900 includes collar 901 that is generally annularlyshaped and includes rounded side wall 904 extending betweenbone-engaging surface 903 and proximal surface 902. Proximal surface 902may include an opening (not shown) with a connection portion, such as athread or taper, e.g. Morse taper, for connection to an articulatingprosthetic component, such as a prosthetic humeral head, and preferablyalso with an instrument to facilitate the removal of the base during arevision surgery, such as by pulling out the implant or using a slaphammer.

Base 900 includes central anchor 940 extending distally frombone-engaging surface 903 and terminating at a distal end or tip 975.Distal tip 975 allows for entry of the implant into the bone, and thedistal tip may be angled between about 60 degrees and about 85 degreesfrom a vertical axis of the central anchor 940, and preferably about 75degrees from the vertical axis.

For purposes of illustration, FIG. 41 has been labeled to show theanterior (“A”), posterior (“P”), medial (“M”), and lateral (“L”)positions of base 900. Base 900 includes four ribs 970, which eachcorresponds to a distinct position of the base. For example, rib 970 ais oriented toward the medial position, rib 970 b is oriented toward thelateral position, rib 970 c is oriented toward the posterior position,and rib 970 d is oriented toward the anterior position. Ribs 970 a and970 b, extending in the medial-lateral direction are substantially inline with one another, and ribs 970 c and 970 d, extending in theanterior-posterior direction are also substantially in line with eachother and are substantially perpendicular to ribs 970 a and 970 b. Assuch, the ribs 970 may be said to define four quadrants of the base.Ribs 970 a and 970 b extend closer to side wall 904 than do ribs 970 cand 970 d. As such, the span across ribs 970 a and 970 b is greater thanthe diameter or span across ribs 970 c and 970 d. As a result, the ribs970 have a greater span in the medial-lateral direction than in theanterior-posterior direction, as best shown in FIG. 41 . Anchor 940includes surfaces 976 extending from distal end or tip 975 tobone-engaging surface 903 and positioned between two adjacent ribs 970.Surfaces 976 are rounded and, in the illustrated embodiment, aregenerally convex.

Each rib 970 includes two opposing lateral side walls 971 and outersurface 973 between the two lateral side walls 971. FIG. 42 shows a sideview of base 900 and more particularly shows the span of side walls 971of the medial rib 970 a and the lateral rib 970 b. As shown in thisview, distal tip 975 transitions into ribs 970. As distal tip 975transitions into medial and lateral ribs 970 a and 970 b, respectively,outer surface 973 is generally convex. The convex shape increases theamount of material for enhanced ingrowth surface and increases therotational stability of the base.

FIG. 43 shows the span of the side walls 971 of the posterior rib 970 cand anterior rib 970 d. As shown in this view, as distal tip 975transitions into posterior and anterior ribs 970 c and 970 d,respectively, outer surface 973 is generally concave, which helps tocompress and accommodate bone during impaction.

Additionally, as seen in FIGS. 42-43 , the width of each outer surface973 of the ribs 970 decreases in the proximal to distal direction. Assuch, the width of the outer surface 973 is wider nearer tobone-engaging surface 903 than to the distal tip 975.

Collar 901 includes a plurality of continuous chisel slots 913 extendingthrough bone-engaging surface 903 to proximal surface 902. In theillustrated embodiment, there are four chisel slots 913 with each chiselslot positioned radially outward of a surface 976 and between twoadjacent ribs 970. Chisel slot 913 is positioned along a path thattracks adjacent to ribs 970 on collar 901, and the portion of eachchisel slot adjacent medial and lateral ribs 970 a and 970 b extendfurther radially outward toward side wall 904 than the portion of eachchisel slot that extends adjacent posterior and anterior ribs 970 c and970 d. As shown in FIG. 41 , each chisel slot 913 is asymmetric about atleast two planes.

Collar 901 includes a plurality of peripheral anchors or pegs 910extending distally from bone-engaging surface 903 to distal tips 920.Pegs 910 are positioned radially outwardly of chisel slots 913, and havesubstantially the same structure as pegs 210 described above withreference to base 200. Pegs 910 are oriented such that when the base isimplanted, the pegs are fixed within the bone near the cortical rim andwithin the cancellous bone. With placement of the pegs 910 within goodquality bone, the pegs aid in the fixation of base 900 to the bone, andmay particularly assist in initial fixation. While there can be anynumber of pegs 910 on collar 901, preferably there are four pegspositioned at substantially equal circumferential intervals around thecollar. As described in greater detail above, the use of four pegs aidsin initial fixation of the implant component with bone duringimplantation.

Like chisel slots 613 of base 600, chisel slots 913 are sized andpositioned to facilitate removal of the base during a revisionprocedure. With chisel slots positioned between anchor 940 and pegs 910,the chisel slots allow for loosening of the bone ingrowth on theenhanced fixation surfaces on ribs 970 and surfaces 976 as well as thebone fixed to the pegs. A chisel tool (not shown) may be similar to tool720 but may have a correspondingly mating shape to fit within the chiselslots 913, may be used to remove the bone from the base to detach thebase therefrom. Additionally, more than one chisel slot may be used atthe same time. As the bone is removed from more than one chisel slot itcreates a form of plug to allow the base to be removed at once. In analternative embodiment (not shown), the chisel slots 913 may be angledto allow a tool to track along a path that closely matches or issubstantially parallel to the longitudinal axis of the anchor 940. Assuch, the profile of the each chisel slot may be perpendicular to collar901.

Collar 901 includes a coating forming an enhanced fixation surface thatmay be a porous metal surface, such as porous titanium alloy. Thefixation surface may facilitate bone ingrowth after impaction and may berougher for greater friction between the enhanced surface and bone foradditional fixation. Portions of base 900 may include at least one layerof an enhanced fixation surface. In the illustrated embodiment, aportion of each side wall 971 of ribs 970 includes an enhanced fixationsurface, and a portion of each surface 976 of the anchor 940 includes anenhanced fixation surface. Specifically, the portions of anchor 940having enhanced surfaces may include three materials. A first, innersurface may be formed of solid metal, such as titanium, the secondsurface may be formed of a porous metal, such as a porous titaniumalloy, such as Tritanium®, and a third and outer surface may be formedof a modified or directional Tritanium®. The outer surface may be formedto increase friction with the bone and may help to increase initialstability. In the illustrated embodiment, between about 30 percent andabout 60 percent, and preferably between about 40 percent and about 50percent, of the total depth of anchor 940 is solid, the depth beingmeasured from the proximal end of the anchor to the distal end. Thissolid portion is in line with the punched cavity and helps to maintainalignment of the base during impaction into the punched cavity. Ofcourse, other portions of base 900, including all or a portion of collar901 may include one or more layers of coatings, alternatively, theentirety of the base may include surface coatings for bone ingrowth.

In another alternative embodiment, as shown in FIGS. 44-46 , anchor 940of base 900 includes a distal portion of enhanced fixation surface onside walls 971 of ribs 970 that includes a porous metal, such as aporous titanium alloy, such as Tritanium®. FIG. 46 shows the distalportion 979 of the ribs having a coating surface 995 of a porous metal,such as porous titanium alloy, such as Tritanium® on a solid metal. Theportion 981 proximal to distal portion 979 includes a first, innersurface 992 of solid metal, a second surface 993 of a porous metal, suchas a porous titanium alloy, and the third, outer surface 994 of modifiedor directional porous metal. Although other arrangements of surfacecoatings are contemplated.

In yet another alternative embodiment, as shown in FIG. 47 , as distaltip 975 transitions into each of the ribs 970, including medial andlateral ribs 970 a and 970 b, outer surface 973 is generally concave.The concavity of the outer surface 973 of the ribs 970 is designed toaccommodate the bicipital groove and maintain a distance therefrom.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A base member of a stemless shoulderimplant, the base member comprising: a proximal collar having a mainproximal surface and a bone-engaging surface opposite the proximalsurface, wherein the proximal collar is annular and defines acontinuously circular outer surface and a continuously circular innersurface; an anchor extending distally from the bone-engaging surface ofthe collar; a central opening in the proximal collar, the centralopening having a taper, the central opening shaped and sized to receivea tapered connector of a prosthetic humeral head to lock the prosthetichumeral head to the base; and an annular rim that defines a continuouslycircular outer surface that is positioned radially inward of thecontinuously circular inner surface of the proximal collar, the centralopening being positioned radially inward of the continuously circularinner surface of the annular rim, wherein a cylindrical recess isdefined between the continuously circular inner surface of the proximalcollar and the continuously circular outer surface of the annular rim,wherein an entirety of the cylindrical recess has a depth extendingdistally of a distal-most surface of the bone-engaging surface of theproximal collar.
 2. The base member of claim 1, wherein a proximal endof the annular rim is flush with the main proximal surface of theproximal collar.
 3. The base member of claim 1, wherein a distal end ofthe central opening terminates in a proximal end of the anchor.
 4. Thebase member of claim 3, wherein the anchor extends from the proximal endof the anchor to a tip at a distal end of the anchor.
 5. The base memberof claim 4, wherein the anchor is solid from the proximal end of theanchor to the tip at the distal end of the anchor.
 6. The base member ofclaim 1, wherein the proximal collar includes a plurality of arcuateapertures.
 7. The base member of claim 6, wherein the plurality ofarcuate apertures includes four arcuate apertures.
 8. The base member ofclaim 7, wherein the plurality of arcuate apertures are spacedequidistantly from the central opening.
 9. The base member of claim 8,wherein the proximal collar includes a plurality of additional aperturespositioned so that each of the plurality of arcuate apertures ispositioned radially between one of the plurality of additional aperturesand the central opening.
 10. The base member of claim 1, wherein theanchor includes four ribs, each of the four ribs having a first endextending from the bone engaging surface of the proximal collar, thefour ribs converging to a tip at the distal end of the anchor.
 11. Thebase member of claim 10, wherein the tip at the distal end of the anchoris positioned along a center longitudinal axis of the base, the centerlongitudinal axis passing through the central opening.
 12. The basemember of claim 11, wherein each of the four ribs is spaced 90 degreesfrom a circumferentially adjacent one of the four ribs.
 13. The basemember of claim 12, wherein each of the four ribs includes two opposinglateral side walls, and an outer surface between the two opposinglateral side walls.
 14. The base member of claim 13, wherein the twoopposing lateral side walls of each of the four ribs includes porousmetal to form an enhanced fixation surface on the two opposing lateralside walls.
 15. The base member of claim 14, wherein the bone-engagingsurface of the proximal collar includes porous metal to form an enhancedfixation surface on the bone engaging surface of the proximal collar.